LS-12-P-2180 Chromatin alterations in pollen: an approach to understand initial mechanism of pollen embryogenesis in Hordeum vulgare

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Pollen embryogenesis (POEM) is an efficient process for the production of doubled haploid plants and represents a convenient model for studying the process of plant cell proliferation in general and embryogenesis in particular. Uninucleate pollen is known to be the most amenable stage for the induction of POEM. Though exact mechanisms are unclear, successful induction of embryogenesis may depend on the epigenetic predisposition of microspores. To elucidate the cellular mechanisms causing gametophytic and embryogenic processes taking place in pollen grains, we have investigated chromatin alterations in both of these pathways. Since gametogenesis is accompanied by distinct chromatin alterations within the nuclei of the vegetative and generative cells (Pandey et al. 2013), it deemed likely that the switch from a gametophytic into an embryogenic pathway is also associated with epigenetic modifications. Immunolabeling confirmed this assumption. Not only did induction of POEM lead to chromatin modifications, typical patterns proved to be very different from those found during gametogenesis. While modifications were restricted to the nucleus during gametogenesis, upon induction of POEM, also the cytoplasm was concerned. Most prominent were the redistributions of the chromatin alterations H3K9ac, H3K4me2 and H3K27me3, all of which play a profound role in transcriptional activity. Inhibition of histone deacetylation by Trichostatin A, not only prevented the redistribution of H3K9ac into the cytoplasm but also that of H3K27me3 and H3K4me2, suggesting an interdependency of these modifications. Since all observed epigenetic alterations take place prior to the first pollen mitosis, they are the earliest known indicators of effective embryogenic induction. Further studies will be required to reveal causal relationships between particular epigenetic signatures and the commencement of POEM. The increased understanding of those mechanisms may eventually contribute to the development of improved haploid technology. References: Pandey et al. (2013) Cytogenet Genome Res DOI: 10.1159/000351211.

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